The invention relates to a method of transmitting data between network devices over a non-deterministic network.
IEEE 802.11 is a standard for wireless networks, which has been used for more than a decade and has created a capability for transmitting wideband data over a wireless interface. Whilst the first generation (IEEE 802.11b) only had limited data throughput, the recent upgrade to IEEE 802.11n has increased this number significantly. With the addition of multiple streams (Multiple Input Multiple Output, MiMo) data throughput has increased to 600 Mbps and will keep on increasing in the future.
Already the first version of IEEE 802.11 gave the opportunity to have a wireless extension to the Ethernet network and also to be able to run all protocols that run on top of the Ethernet physical layer (such as IP, TCP/IP and UDP/IP) on top of the 802.11 PHY/MAC (physical layer/Media Access Control).
For the (wired) Ethernet network there are various protocols to transmit media data, particularly with a low latency (e.g. CobraNet, Dante, Ravenna, AVB, Livewire). All of these protocols have specific requirements on latency, packet rate and bandwidth.
One of the key characteristics of the 802.11 MAC (Media Access Control) is that it uses a so called Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) channel access mechanism. A multitude of network devices can be connected to the same transmission medium to transmit over it and to share its capacity. This mechanism causes non-determinism in the actual data transfer. Thus, those kinds of networks are referred to as non-deterministic networks. Apart from wireless networks, other examples of such non-deterministic networks are bus networks, ring networks, star networks or half-duplex point-to-point links.
With this multitude of network devices sharing the non-deterministic networks, it is not possible to determine, whether a network device can access the medium. Moreover, it is difficult or can even be impossible to predict, whether a network device is able to transmit data over the non-deterministic network. If a media data (media data packet) is sent to the network interface then the actual transmission might be delayed depending on whether the non-deterministic medium is sensed as busy or not.
Traditional media/data streaming applications take care of this non-determinism by adding (large) data buffers and only start playback when the buffer is filled. This however adds a lot of latency (often in the range of is or more) to the media/data stream. Moreover, these known implementations were designed for wired networks and are usually not compatible with non-deterministic networks. Because of this non-determinism it is not realistic to send the above mentioned low latency protocols over a non-deterministic network using a CSMA like MAC (like e.g. 802.11) and achieve a good performance.
Thus, the task of the invention is to provide a method to transmit data, particularly low latency media data, over a non-deterministic network and achieve a good performance and a low latency.